diff --git a/setup.py b/setup.py
index c293a54..07770f8 100755
--- a/setup.py
+++ b/setup.py
@@ -40,6 +40,7 @@ def get_version():
         'GitPython~=2.1.11',
         'typing~=3.6.6 ; python_version<"3.5"',
         'autopep8~=1.4',
+        'six',
     ],
     extras_require={
         ':python_version>="3.0"': [